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931.
Stefan Hagemann Holger Göttel Daniela Jacob Philip Lorenz Erich Roeckner 《Climate Dynamics》2009,32(6):767-781
For the fourth assessment report of the Intergovernmental Panel on Climate Change (IPCC), the recent version of the coupled
atmosphere/ocean general circulation model (GCM) of the Max Planck Institute for Meteorology has been used to conduct an ensemble
of transient climate simulations These simulations comprise three control simulations for the past century covering the period
1860–2000, and nine simulations for the future climate (2001–2100) using greenhouse gas (GHG) and aerosol concentrations according
to the three IPCC scenarios B1, A1B and A2. For each scenario three simulations were performed. The global simulations were
dynamically downscaled over Europe using the regional climate model (RCM) REMO at 0.44° horizontal resolution (about 50 km),
whereas the physics packages of the GCM and RCM largely agree. The regional simulations comprise the three control simulations
(1950–2000), the three A1B simulations and one simulation for B1 as well as for A2 (2001–2100). In our study we concentrate
on the climate change signals in the hydrological cycle and the 2 m temperature by comparing the mean projected climate at
the end of the twenty-first century (2071–2100) to a control period representing current climate (1961–1990). The robustness
of the climate change signal projected by the GCM and RCM is analysed focussing on the large European catchments of Baltic
Sea (land only), Danube and Rhine. In this respect, a robust climate change signal designates a projected change that sticks
out of the noise of natural climate variability. Catchments and seasons are identified where the climate change signal in
the components of the hydrological cycle is robust, and where this signal has a larger uncertainty. Notable differences in
the robustness of the climate change signals between the GCM and RCM simulations are related to a stronger warming projected
by the GCM in the winter over the Baltic Sea catchment and in the summer over the Danube and Rhine catchments. Our results
indicate that the main explanation for these differences is that the finer resolution of the RCM leads to a better representation
of local scale processes at the surface that feed back to the atmosphere, i.e. an improved representation of the land sea
contrast and related moisture transport processes over the Baltic Sea catchment, and an improved representation of soil moisture
feedbacks to the atmosphere over the Danube and Rhine catchments. 相似文献
932.
Jennifer M. Mangan Jonathan T. Overpeck Robert S. Webb Carol Wessman Alexander F. H. Goetz 《Climatic change》2004,63(1-2):49-90
The Nebraska Sand Hills exist in a semi-arid climatic environment and the land surface is grassland growing on sandy soils. These soils have been periodically active throughout the Holocene, but are currently stabilized by the vegetation. However, a shift in climate could cause grassland death and eventual sand dune remobilization. Our studies used the CENTURY nutrient cycling and ecosystem model to investigate the impacts of drought, plant functional type, fire, grazing, and erosion on Nebraska Sand Hills vegetation and dune stability. Fire and grazing alone had little impact on the vegetation, but when combined with mild drought, biomass decreased. Overall biomass increased if one plant functional type was allowed to dominate the ecosystem. Addition of as little as 1 mm of erosion per year under current climate conditions decreases vegetation as much as a drought 20 percent drier than the worst of the 1930s drought years in Nebraska. 相似文献
933.
Adaptive Governance and Climate Change in the Tropical Highlands of Western South America 总被引:2,自引:1,他引:2
Climate changes occurring during the past several decades in the high elevations of the tropical Andes Mountains have implications for the native plant and animal species, for the ecological integrity of the affected land cover, and for the human-biophysical systems involved. Consequences are also probable for rural inhabitants and their livelihoods, especially for farmers and pastoralists. Biophysical factors have always changed in these mountainous zones; the extent and degree of alteration acting on native and agricultural biodiversity is the concern. Addressing these climate changes is probably within the adaptive capacity of many local land-use systems, unless external socioeconomic or political forces are unsupportive or antagonistic. Suitable programs to provide information, subsidies, or alternatives could be designed. We highlight some of the inherent resiliencies of natural and cultural systems in the Andes and suggest that these systems contain lessons that could be useful elsewhere, in terms of the traits that allow for the sustainable utilization of dynamic and heterogeneous landscapes. 相似文献
934.
Harald J. Beine Daniel a. Jaffe John a. Herring Jennifer a. Kelley Terje Krognes Frode Stordal 《Journal of Atmospheric Chemistry》1997,27(2):127-153
Springtime measurements of NOx, ozone, PAN,J(NO2), and other compounds were made near Ny-Ålesund,Svalbard (78°54N, 11°53E), in 1994 and Poker Flat,Alaska (65°08N, 147°29W), in 1995. At Svalbard medianmixing ratios for PAN and NOx of 237 and 23.7 pptv,respectively, were observed. The median mixing ratios at Poker Flat for PANand NOx were 79.5 and 85.9 pptv, respectively. These data areused to estimate thermal PAN decomposition using several differentapproaches. At Svalbard PAN decomposition was very small, while at PokerFlat up to 30 pptv/h PAN decomposed. At both sites the NOx/PANratio increased with temperature between –10 and 20°C implyingthat PAN decomposition is an important NOx source. In-situozone production was calculated from the measured NO, NO2,O3, J(NO2), and temperature data, using thesteady state assumption Median ozone production was 605 pptv/h at PokerFlat, and one order of magnitude smaller at Svalbard during the daytime.Only at Poker Flat could a direct influence on the diurnal ozone cycle beobserved from in-situ production. These results imply that PAN decompositionis a major source of NOx in the high latitude troposphere, andthat this contributes to the observed spring maximum in surface ozone. 相似文献
935.
T. H. Boller H. Lorenz V. L. Afanas'Ev S. N. Dodonov V. Yu. Terebizh 《Astronomische Nachrichten》1989,310(3):187-193
Zwei ausgewählte Felder (südöstlich der Galaxie M 82 und in SA 57) werden vollständig spektroskopisch nach Quasaren durchmustert. Die (N — m)-Relation wird um 0.4 bzw. 1.6 Größenklassen in bezug auf den von KRON und CHIU (1981) bestimmten Werte erweitert. Konsequenzen für Modelle der Entwicklung der Leuchtkraftfunktion werden diskutiert. 相似文献
936.
937.
938.
L. Erculiani-Abati V. L. Afanasjev O. Spiridonova H. Lorenz 《Astronomische Nachrichten》1989,310(2):97-102
We present spectroscopically confirmed quasars in the 25 sq. degrees A1-field to a limiting magnitude of mB = 18.0. Our estimate of the quasar density of 0.28 ± 0.11 objects per sq. degree based on the “complete” sample of A1-qusars is in agreement with the observed integral number-magnitude relation. However, we consider this value as still a lower limit of the quasar density in the A1-field due to the uncertainties during the colour based selection of objects, especially their brightness dependence, resulting in serious selection effects. Thus, the quasar density of the A1 survey may be underestimated up to 30% and does not contradict the recently estimated incompletness of the BQS survey. 相似文献